High-frequency dual-channel lock-in detection via rapidly oscillating driving

Research Question and Approach

Conventional quantum sensing protocols for detecting ac signals, such as those based on dynamical decoupling, are typically limited by the finite Rabi frequency of the control pulses. When the target signal frequency exceeds this limit, pulse duration becomes comparable to the signal period, leading to significant performance degradation. This paper addresses this limitation by proposing a dual-channel lock-in detection protocol that utilizes rapidly oscillating driving fields to modulate the interaction between a quantum probe and a high-frequency target signal. By applying a driving field at the same frequency as the target signal, the authors derive an effective static Hamiltonian that allows for the simultaneous extraction of the signal's amplitude and initial phase.

The researchers demonstrate that by setting the Rabi frequency of the driving field to a rapidly oscillating trigonometric function, the system's evolution can be described by an effective Hamiltonian proportional to the product of the signal and driving amplitudes. This mechanism enables the measurement of high-frequency signals far beyond the probe's inherent Rabi frequency limit. The protocol requires only two population measurements to determine both the amplitude and phase, significantly improving detection efficiency compared to traditional statistical methods. Numerical simulations using nitrogen-vacancy (NV) centers in diamond confirm that the protocol effectively filters out background noise—including white, 1/f, and harmonic noise—resulting in a substantial improvement in the signal-to-noise ratio (SNR).

This protocol provides a robust, noise-resistant method for high-frequency signal detection, extending the operational range of quantum sensors. By eliminating the need for complex statistical analysis and overcoming the frequency constraints imposed by finite pulse durations, this approach enhances the utility of quantum platforms like NV centers for applications in magnetic resonance spectroscopy and electromagnetic-field characterization.